One of the two Indian men arrested for illegally buying mobile phone cards used by the gunmen in the Mumbai attacks was a counterinsurgency police officer who may have been on an undercover mission, security officials said Saturday, demanding his release.

The arrests, announced in the eastern city of Calcutta, were the first since the bloody siege ended. But what was touted as a rare success for India’s beleaguered law enforcement agencies, quickly turned sour as police in two Indian regions squared off against one another.

Senior police officers in Indian Kashmir, which has been at the heart of tensions between India and Pakistan, demanded the release of the officer, Mukhtar Ahmed, saying he was one of their own and had been involved in infiltrating Kashmiri militant groups.

Indian authorities believe the banned Pakistani-based militant group Lashkar-e-Taiba, which has links to Kashmir, trained the gunmen and plotted the attacks that left 171 people dead after a three-day rampage through Mumbai that began Nov. 26.

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The implications of Ahmed’s involvement — that Indian agents may have been in touch with the militants and perhaps supplied the SIM cards used in the attacks — added to the growing list of questions over India’s ill-trained security forces, which are widely blamed for not thwarting the attacks.